The present invention relates to a method of manufacturing a trench isolation, more specially to a method of manufacturing a trench isolation which can prevent formation of void in narrow trench and the difference of height between narrow trench and wide trench, thereby preventing a short of conducting line and an increase of a parasitic .capacity and a fall of characteristic of MOS transistor.
A method of manufacturing a trench isolation is generally composed of steps which a trench is formed in a semiconductor substrate, thereafter CVD oxide layer is deposited on a trench and an upper side of a semiconductor substrate, thereafter the entire structure is flatly covered by a photoresist, thereafter a photoresist and a CVD oxide layer is etched on condition that the photoresist/CVD oxide layer etch ratio is 1 and CVD oxide layer only remains in a trench.
FIGS. 1A to 1D show steps in manufacturing a conventional trench isolation.
Referring to FIG. 1A, the 1st oxide layer 21 and nitride layer 22 and the 1st photoresist 23 are sequentially formed on the silicon substrate 1, thereafter the pattern of the 1st photoresist 23 is formed by eliminating an intended part of the 1st photoresist 23, and the 1st oxide layer 21 and nitride layer 22 of the eliminated part of the first photoresist 23 is etched. Continuously narrow trench 10 and wide trench 10' is formed by etching silicon substrate 1.
Referring to FIG. 1B, the 1st thermal oxide layer 24 is formed on the side and bottom wall of trench 10,10', thereafter the 2nd oxide layer 25 is thickly formed on the entire structure.
It is noticeable that an etch ratio increase in case of wet etching because the void is formed at the central part of the 2nd layer 25.
Referring to FIG. 1C, the second photoresist 26 is flatly coated on the entire structure. Referring to FIG. 1D, the second photoresist 26 and the 2nd oxide layer 25 is etched until the nitride layer 22 is exposed on condition that the 2nd photoresist/the 2nd oxide layer etch ratio is 1. Thereafter, a trench isolation 25A including the 2nd oxide layer 25 is formed by eliminating the nitride 22 and the 1st oxide layer 21 in HNO.sub.3 or hot H.sub.3 PO.sub.4 solution. A void is formed in narrow trench isolation 25A when an etch back process and a wet etch is performed and a topology having a length of "d" is formed in a wide trench isolation 25B.
In the conventional method as described above, problems are as follows:
First, the possibility is high which a conducting line is short because of a void. Second, the characteristic of MOS-transistor falls since the difference of height is formed between a wide trench isolation and a narrow trench isolation.
Third, a device does not have high speed since a parasitic capacity increases. As disclosed in Japanese application No. sho 62-289954 for the purpose of solving problems of conventional method, a method of manufacturing a trench isolation has been proposed.
Referring to FIGS. 2A to 2F, a method of manufacturing of Japanese application is described as follows.
Referring FIG. 2A, mask layer 1b and the first resist layer 1c is formed on the silicon substrate 1a, thereafter the pattern is formed as an intended size. Referring FIG. 2B, narrow trench and wide trench are formed on the silicon substrate 1a, thereafter, resist layer 1c is eliminated. Referring FIG. 2C, the 1st thermal oxide layer 5 and polysilicon layer 7 are sequentially formed on the silicon substrate 1a after said mask layer 1b is eliminated.
Referring FIG. 2D, as polysilicon layer 7 is oxidized by heat, a groove of narrow trench 10 and wide trench 10' is filled because of volume increase. Therefore, the inner part of trench 10, 10' is filled in the 2nd thermal oxide layer 7'.
Referring FIG. 2E, resist 1d is flatly coated by spin on the entire structure. Referring FIG. 2F, resist 1d and the 2nd thermal oxide layer 7' is etched by reactive ion which resist 1d/the 2nd thermal oxide layer 7' etch ratio is approximately 1.
However, a conventional method of manufacturing a trench isolation can prevent formation of void in narrow trench, but cannot prevent formation of the difference of height between narrow trench and wide trench by over etching wide trench.